Electrical printing apparatus using screen with thick coating to define image



I May 6, 1969 Filed June 5. 1965 W. E. JOHNSON ELECT AL PRINTINGAPPARATUS USING SCREEN WI THICK COATING TODEFINE IMAGE M Sh eefg,

lnuezzlor. MLLIQM E. JOHNSON wN/Z P461104 HrTOE/VfV-S May 6, 1969 w. E.JOHNSON INTING APPARATUS US WITH THICK COATING TO DEFINE 1m SCREEN IMAGEELECTRICAL PR Sheet Filed June 5, 1965 United States Patent ELECTRICALPRINTING APPARATUS USING SCREEN WITH THICK COATING T0 DEFINE IMAGEWilliam E. Johnson, Temperance, Mich., assignor to Owens-Illinois,Incorporated, a corporation of Ohio Filed June 3, 1965, Ser. No. 461,126Int. Cl. B41f 15/00 US. Cl. 101114 4 Claims ABSTRACT OF THE DISCLOSUREProcesses of the general type with which the present invention isconcerned are disclosed in my co-pending applications Ser. Nos. 393,817,now abandoned, and 439,799 now Patent No. 3,301,179 issued Jan. 31,1967, filed Aug. 31, 1964, and Mar. 15, 1965, respectively, and assignedto the assignee of the present application.

The present invention is, in general, directed to improvements instencil screens employed in such processes.

One object of the present invention is to provide a stencil screen foruse in electrical decorating processes of the type referred to abovewhich achieves an extremely high degree of resolution and sharpness inthe powder image applied to the article.

It is another object of the invention to provide stencil screens capableof applying a sharply defined multicolor image of uniform density andthickness.

It is another object of the present invention to provide methods andapparatus for electrically applying an imageshaped layer of printingpowder particles to a non-conductive article surface.

It is another object of the invention to provide improved stencilscreens and methods for preparing such screens.

It is another object of the invention to provide an improved method forpreparing stencil screens adapted to apply image-shaped layers ofprinting powder particles of different colors in adjacent or abuttingrelationship to each other on an article surface with a high degree ofimage resolution.

Other objects and features of the invention will become apparent byreference to the following specification and to the drawings.

In the drawings:

FIGURE 1, is a schematic diagram, partially in cross section, of apresently known electrical printing process;

FIGURE 2, is a schematic diagram, similar to FIG- URE 1, showing oneform of the present invention;

FIGURE 3, is a schematic diagram, partially in section, of a second formof the invention;

FIGURE 4, is an elevational view of one of two stencil screens employedin a two color decorating process;

FIGURE 5, is a schematic cross sectional diagram showing a portion ofthe screen of FIGURE 5 and a sectional view of the image applied therebyto an article 3,442,207 Patented May 6, 1969 surface, the section beingtaken approximately on the line 5-5 of FIGURE 4;

FIGURE 6 is an elevtional view of the mating stencil screen employed inconnection with the screen of FIG- URE 4 in the two color decoratingprocess;

FIGURE 7, is a sectional view similar to FIGURE 5, showing the stencilof FIGURE 6 and a cross section of the resultant image;

FIGURE 8, is an elevational View of one of two stencils employed in asecond two color decorating operation;

FIGURE 9, is a sectional view, similar to FIGURE 5, of the stencil ofFIGURE 8 and its resultant image;

FIGURE 10, is an elevational view of the second stencil employed inconjunction with the stencil of FIG- URE 8; and

FIGURE 11, is a cross sectional view of the stencil of FIGURE 10 and itscorresponding image.

In FIGURE 1 of the drawings, there is schematically illustrated anarrangement for applying an image-shaped layer of printing powderparticles to the surface of an article A in accordance with theteachings of my copending application Ser. No. 439,799, filed Mar. 15,1965, and assigned to the assignee of the present application. Theapparatus disclosed in FIGURE 1 includes a platelike support 20 ofelectrically conductive material upon which is supported a looselypacked bed of printing powder particles 22. A stencil screen designatedgenerally 24 is supported at a pre-selected distance above the surfaceof bed 22, while the article A is in turn supported above screen 24 at aselected distance as by electrically nonconductive spacers 26.

Stencil screen 24 is preferably constructed with a metallic frame 28which supports an open mesh wire screen 30 having mesh openings largerthan the maximum size of powder particles in bed 22. A coating 32 isapplied to a portion of screen 30 to fill and mask the mesh openings andan uncoated portion 34 of the screen is provided to define animage-shaped aperture through which powder particles can pass from bed22 to the surface of article A.

Screen 24 may be prepared in accordance with the teachings of UnitedStates Patents Nos. 3,100,150, 3,170,- 791 or 3,170,792. In general, theprocess of preparing a screen 24 includes the steps of applying acoating of a material such as those specified in the above-mentionedpatents to the entire area of screen 30. The various coatings include alight sensitizing agent which, when exposed to light, transforms thecoating material from a water soluble state to a water insoluble state.The coated screen is then covered with an opaque positive film of thedesired design and exposed to light. After exposure, the exposed screenis Washed with water, and the coating on the nonexposed portions of thescreen is dissolved, thereby forming the image-defining aperture 34.

As described in detail in my above-mentioned application Ser. No.439,799, suitable voltage sources V1 and V2 are electrically connectedto powder bed support plate 20, the wire mesh 30 and to article A asillustrated in FIG- URE 1. A pulse time control circuit schematicallyindicated at 36 is employed to control the time period of energizationof voltage sources V1 and V2. Voltage sources V1 and V2 when energizedelectrically charge powder particles in bed 22 and establish an electricfield extending from the upper surface of the powder bed support 20 toto the registered surface of article A. The charged particles areimpelled by the electric field to pass upwardly 3 from powder bed '22toward-the surfaceof article A. The masked portion of stencil 24 definedby coating 32 restricts the passage of particles to the surface ofarticle A to those particles which pass through image aperture 34.

Because the opposed surfaces of article A and powder bed support plate20 are parallel to each other, the lines of force of the electric fieldextend vertically in straight lines and hence those particles whichreach the surface of article A are deposited on the article surface overan area corresponding in size and shape to that of image aperture 34.

Pulse time control circuit 36 functions in a manner described in detailin my co-pending application Ser. No. 439,799 to automaticallyde-energized voltage sources V1 and V2 when a predetermined quantity ofparticles, representing an image-shaped layer of preselected thickness,is deposited upon the surface of article A.

While the electric field configuration is such that particlestransferred from bed 22 to the surface of article A tend to travel instraight vertical paths, several effects are present which tend todivert the particles from truly vertical paths. Among these effects areair currents, electric field gradients, interparticle repulsion,retransfer and mechanical collisions.

Air currents are generated due to the fact that a large number ofparticles are impelled substantially simultaneously through a relativelyconfined space, while electric field gradients exist because of thepresence of the wire mesh in aperture 34 which causes the electric linesof force to be deflected toward the individual wires.Particleto-particle repulsion exists because of the like nature of thecharges on the individual particles, while mechanical collisions betweenparticles are unavoidable. Retransfer occurs when a particle reachingthe surface of article A loses its original charge and becomes chargedin the reverse sense by virtue of its contact with the article surfaceand is thereby repelled, further increasing the probability ofmechanical collision. All of these effects tend to decrease imageresolution by scattering particles in transit in a manner such that someof the particles strike the article surface at locations out of avertical registry with image aperture 34, thereby producing a lack ofsharpness around the edges of the applied image.

The degree of resolution attainable in the arrangement shown in FIGURE 1is a function of the gap or spacing between screen 30 and the surface ofarticle A. The larger the gap, the less resolution can be achieved.

In FIGURE 2, one embodiment of the present invention is disclosed inwhich a stencil 24 is constructed with a coating 32' on the upper sideof screen 34' which is of a thickness sufficient to perform the functionof spaces 26 in the FIGURE 1 embodiment. With the exception of thethickened coating 32' on the upper side of screen 34', the arrangementis the same as that of FIGURE 1.

As described in United States Patents 3,100,150, 3,170,- 791 and3,170,792, the various coatings may be applied to the screen by asqueegee, a normal application of the coating in this manner usuallyresulting in a coating having a thickness of approximately one mil. Thethickened coating 32' of the FIGURE 2 embodiment is achieved by applyingthe coating several layers, drying the coating between the applicationof successive layers. In this manner, a coating of the desired thicknessmay be built up on one side of the screen mesh 34. The coating materialsare sufficiently transparent that the formation of the image aperturemay be accomplished by the photographic exposure and washing techniquedescribed in the three patents referred to above.

The thickness of coating 32' is chosen in accordance with the desiredimage density or thickness of the layer of particles deposited upon theSurface of article A. In normal glass decorating processes, the usuallydesired thickness of the image-shaped layer of particles applied to thearticle surface is approximately to 6 mils, and the thickness of coating32 in such case would be approximately 8 mils, as measured from theupper side of screen 30. As explained above, the thickness of the imagshaped layer of particles applied to the surface of article A isaccurately regulated by the pulse time control circuit 36 as describedin detail in my co-pending application Ser. No. 439,799.

In FIGURE '3, there is disclosed a further embodiment of the inventionespecially adapted to decorate the surface of an article A ofelectrically non-conductive material. In the previously describedembodiments of FIG- URES 1 and 2, the article A must, in order toperform its function as an equipotential surface of the electric field,possess a reasonable degree of electrical conductivity. In manyinstances, it is desired to decorate an article, such as a plasticbottle for example, which is constructed of a material which for allpractical purposes is electrically non-conductive.

In FIGURE 3, a stencil designated generally 124 is supported, as in theFIGURE 1 embodiment, between an electrically conductive powder bedsupport 20 upon which is supported a loosely packed bed 22 of printingpowder particles. In the embodiment of FIGURE 3, the frame 126 ofstencil 124 is constructed of an electrically nonconductive material anda wire mesh 130 is fixedly secured within frame 126. The screen coating132 is applied in several successive layers, as in the FIGURE 2embodiment, to provide a coating of selected thickness above the uppersurface of screen 130 and the image aperture 134 is formed as describedabove. On the upper surface of the thickened screen coating 132, a layerof electrically conductive material 136 is applied, the conductivematerial 136 being applied only to the upper surface of coating 132 andnot extending downwardly along the side edges of image aperture 134. Theconductive layer 136 may take the form of a relatively thin metallicfoil or may be applied by coating the upper surface of the stencilcoating 132 with an electrically conductive paint.

In this embodiment, the combined thickness of stencil coating 132 andconductive layer 136 constitutes the predetermined thickness of spacingbetween the surface of article A and screen 130. In the FIGURE 3embodiment, voltage source V2 is electrically connected to theconductive layer 136 instead of to the article as in the previousembodiment. Because the screen frame 126 in the FIGURE 3 embodiment iselectrically non-conductive, the electrical connection is made directlyto the wire mesh.

In operation, voltage sources V1 and V2 are energized as in the FIGURE 1embodiment, thereby establishing an electric field having a hole in theuppermost electrode of the field constituted by conductive layer 136. Inthe FIGURE 3 embodiment, the field strength of the lower field-the fieldbetween powder bed support 20 and screen 130is strong enough so thatparticles are accelerated through the screen in image aperture 134 withsufficient velocity to reach the surface of article A. As a layer ofparticles begins to be formed on the surface of article A within imageaperture 134, the particles effectively bridge the gap or opening andthus, in effect, electrically fill the hole in upper electrode 136.Electrode 136 dissipates the charge on those particles with which it isin direct or indirect electrical contact and the particles adhere to thesurface of article A by the mechanical compaction of the layer. As inthe previous embodiment, pulse time control circuit 36 acts tode-energize voltage sources V1 and V2 when a predetermined quantity orthickness of particles has been accumulated on the surface of article A.4

All of the embodiments described above have been disclosed in connectionwith the formation of a single color image on the article surface. Themanner in which the thickened stencil coating is formed in the FIGURES 2and 3 embodiments enables a convenient method for forming multicolorimages having a high degree of reso lution. In FIGURES 4 through 7, theapplication of the FIGURE 2 embodiment to a multicolor image is shown inone exemplary form, while FIGURES 8 through 11 inclusive show a similarapplication of the FIGURE 3 embodiment to a multicolor image. In bothinstances, the ultimate image is assumed to be a circular image crossedby a diametrically extending diagonal stripe, with the stripe being ofone color and the remainder of the circular background of a secondcolor.

Referring first to FIGURES 4 through 7, two stencils are employed toform a smooth surfaced layer of particles in the form of a two colorimage on the surface of a conductive article A. In FIGURE 4, the firststencil 150 is shown in elevation having a two part image aperture 152in the shape of the background portion of the ultimate image to be of afirst color. The coated or masked portion of the stencil includes thediagonal strip 154 extending between the two parts of image aperture152, strip 154 corresponding to the diagonal stripe of the image whichwill be of the second color. The stencil 150 is prepared in the mannerdescribed above in connection with the FIGURE 2 embodiment and, as bestseen in the cross sectional view of FIGURE 5, the stencil coating isthickened on the article surface side of the stencil to provide thedesired spacing between the stencil screen wire 156 and the surface ofarticle A.

The first color portions of the image, corresponding in shape to imageaperture 152 are then applied to the article surface by placing thearticle surface in contact with the stencil and establishing theelectric field as described above. In FIGURE 5, a sectional view of thearticle A with the first color image portions 158 applied is shownseparated from the stencil.

The second stencil 160 is shown in elevation in FIG- URE 6. Stencil 160is formed with an image aperture 162 formed in accordance with thedimensions of the diagonal stripe in the ultimate image. As best seen inthe sectional view of FIGURE 7, the stencil coating is formed with acircular recess 164 which extends inwardly from the article facingsurface of the stencil coating to a depth equal to or slightly greaterthan the thickness of the previously applied image portions 158.

Stencil 160 is so formed in the following manner. Assuming that an eightmil spacing is desired between the wire mesh of the stencil and thearticle surface, and that the desired image layer thickness is fivemils, the wire mesh of stencil screen 160 is first coated with twolayers of a coating of the type described in United States Patents Nos.3,100,150, 3,170,791 or 3,170,792 and is then exposed through a positivefilm having a diagonal opaque stripe corresponding to image aperture162. The exposed stencil is then washed in water to form a stencilhaving a coating approximately two mils in thickness with an imageaperture in the shape of aperture 162 through the coating.

Additional layers of coating are then applied until the desired coatingthickness of eight mils is achieved. A positive film having an opaquecircular portion is then placed on the coated stencil in registry withthe diagonal stripe portion 162 and again the stencil is exposed tolight. A second washing operation results in recess 164. The bottom ofrecess 164 is formed by the surface of the second layer of coating whichwas rendered water insoluble by the original exposure.

The stencil 160 is then carefully placed in registry with the previouslyapplied image layer 158, aperture 162 registering with the space betweenthe two previously applied image layers 158. A powder transfer operationas described above is then performed with the second color of powder toachieve the desired image. The resulting image is smooth surfaced inthat both color portions of the image are layers of the same thicknessThe electrical transfer conditions are the same in each case because themesh to surface spacing is the same.

In FIGURES 8 through 11, a generally similar process for applying thesame two color image to a non-conductive article A is illustrated. Inthis case, it is somewhat more convenient to apply the diagonal stripefirst and the background color second. This is because in applying thediagonal stripe first, the electrically conductive layer 186 is incontact with the powder of the diagonal stripe entirely around theperiphery of the stripe during its application. Similar electricalcontact is achieved on the circular portions of the periphery of thebackground in the second powder application. While electrical contactwill exist between the first and second applied powder layers, theelectrical conductivity of the powder is no where near as great as thatof the electrically conductive layer. By proceeding in the manner shownin FIGURES 8 through 11, the maximum amount of direct contact betweenthe electrically conductive layer or coating on the stencil and thepowder actually being: applied is achieved.

As indicated in FIGURES 8 and 9, a stencil having the diagonal stripeportion of the image defined by an image aperture 172 is made in themanner described in connection with FIGURE 3 above and the diagonalstripe portion 174 of the image is applied. The second stencil is madeaccording to the technique described above in connection with stencil160, the difference being only in that the masked and unmasked portionsof the image aperture 182 are reversed as compared to the FIGURE 6embodiment. In the completed stencil 180, the masked portion 184representing the diagonal stripe has a thickness of two mils while thecombined thickness of the coating and conductive layer 186 will be theeight mils of the example. In order to prevent undue distortion of theelectric field, it is preferable not to apply a conductive layer to thediagonal masked portion 184 because of the close proximity of thissurface to the wire mesh of the stencil.

While I have described certain embodiments of the invention in detail,it will be apparent to those skilled in the art that the disclosedembodiments may be modified. Therefore, the foregoing description .is tobe considered exemplary, rather than limiting, and the true scope of theinvention is that defined in the following claims.

I claim:

1. For use in an apparatus for applying a second imageshaped layer ofpredetermined thickness composed of printing powder particles of a firstcolor and a known size range to an article surface in adjacent registrywith a previously applied first image shaped layer of the same thicknessof particles of a different color; a stencil having an image-definingaperture therethrough comprising an open mesh screen having meshopenings larger than the maximum size of powder particles in said knownsize range, a coating filling and masking the mesh openings of saidscreen over a first portion only of said screen, the remaining portionof said screen constituting said image-defining aperture correspondingin shape to said second image-shaped layer, said coating on one side ofsaid screen being of a thickness greater than the predeterminedthickness of the layer of particles to be applied to an article surfacewhereby the screen mesh is positioned at a preselected spacing from thearticle surface when the coating at said one side of said screen isengaged with the article surface, and means defining a recess in saidcoating corresponding in shape to said first image shaped layer andhaving a depth at least equal to the thickness of said first layer.

2. A stencil as defined in claim 1 further comprising a layer ofelectrically conductive material on the surface of said coating.

3. Apparatus for electrically applying an image-shaped layer ofpredetermined thickness composed of printing powder particles capable ofbeing electrically charged and having sizes falling within a given sizerange, said apparatus comprising a bed of printing powder particles ofsaid given size range, an electrically conductvie open mesh screenhaving mesh openings of a uniform size larger than the maximum size ofsaid particles, an electrically non-conductive coating on one side ofsaid screen filling the screen openings over a first portion of saidscreen to define a masked portion surounding an unmasked portion of saidscreen constituting an image-defining aperture through said coating,said coating being of a thickness greater than the predeterminedthickness of the layer of printing powder particles, means supportingsaid screen in a preselected spaced relationship to said bed of printingpowder particles with said coating on the side of said screen remotefrom said bed, means for supporting an article in contact with saidcoating with the article surface extending across said image-definingaperture, electric power supply means electrically connected to saidscreen and operable, when energized, to establish an electric fieldbetween said bed and said article surface operable to electricallycharge powder particles in said bed and to impel charged particles fromsaid bed through said image defining aperture in said coating to saidarticle surface, said coating confining the particles to that portion ofsaid article surface exposed to said bed by the aperture in saidcoating, and means operable upon energization of said electric powermeans for de-energizing said power :means when a layer of particles ofsaid predetermined thickness has been applied to said article surface.

4. Apparatus as defined in claim 3 for applying said image-shaped layerto said article surface in adjacent 25 relationship to a previouslyapplied layer of particles, said stencil coating having a recess thereinextending inwardly from the side of said coating remote from said screento a depth equal to or greater than the thickness of said previouslyapplied layer of particles and less than the thickness of said coating,said recess being in the shape of the first applied layer of particles.

References Cited UNITED STATES PATENTS 839,187 12/1906 Norton 117-232,787,556 4/1957 Haas 11717.5 2,940,864 6/ 1960 Watson 117-17.53,228,326 1/ 1966 C-hildrcss 1011 14 3,241,483 3/1966 D-ulf l0 1-1293,245,341 4/1966 Childress et al 101-122 3,253,540 5/1966 Lusher 101-170 3,294,017 12/1966 St. John 101114 3,301,179 1/1967 Johnson 101-114EDGAR S. BURR, Primary Examiner.

US. Cl. X.R. 101-127, 129

